The present invention relates to a displacement control structure for a variable displacement compressor.
The variable displacement compressor as disclosed by Japanese Patent Application Publication No. 2001-355570 or No. 2004-197679 detects if the flow rate of refrigerant is appropriate and controls the valve opening of the displacement control valve thereof. The latter reference discloses the displacement control valve whose valve opening is changed by difference of pressure between two points upstream and downstream of the throttle provided in a passage for discharge refrigerant. In the displacement control valve, urging force caused by the pressure difference is opposed to electromagnetic force generated by applying electric current to a solenoid through a valve body, and the valve body is arranged so as to be balanced between the urging force caused by the pressure difference and the electromagnetic force thereby to specify the valve opening.
The above pressure difference increases as the refrigerant flow rate increases. The pressure difference reflects the refrigerant flow rate, and in the variable displacement compressor the valve opening increases as the pressure difference increases. When the refrigerant flow rate exceeds an appropriate flow rate, the valve opening increases thereby to increase the flow rate of refrigerant supplied from the discharge chamber to the crank chamber through the valve hole. This causes the pressure in the crank chamber to be risen thereby to decrease inclination angle of the swash plate, which decreases the refrigerant flow rate so as to converge to the appropriate flow rate. When the refrigerant flow rate becomes lower than the appropriate flow rate, the valve opening decreases thereby to decrease the flow rate of refrigerant supplied from the discharge chamber to the crank chamber through the valve hole. This causes the pressure in the crank chamber to be fallen thereby to increase the inclination angle of the swash plate, which increases the refrigerant flow rate so as to converge to the appropriate flow rate.
The displacement control valve is built in the rear housing and the throttle is provided in a conduit of an external refrigerant circuit.
In the structure where the displacement control valve is built in the rear housing, however, passages are complicatedly formed. In the passages are included a passage through which pressure of the refrigerant upstream of the throttle of the conduit of the external refrigerant circuit acts on the displacement control valve, a passage through which the pressure of refrigerant downstream of the throttle acts on the displacement control valve, and a passage through which the refrigerant is supplied from the displacement control valve to the crank chamber. In addition, although a passage forming portion is needed for ensuring a part of these passages in the rear housing, the passage forming portion which forms a part of the rear housing causes the weight of the rear housing to be increased, which increases the weight of the compressor.
The present invention is directed to a displacement control structure which prevents structural complexity of passages through which pressure of the refrigerant upstream and downstream of the throttle respectively act on the displacement control valve, and which also prevents the increase of the weight of the variable displacement compressor.